9-Alkenyl esters, such as 9-dodecadienyl acetate, 9-tetradecenyl formate, 9-tetradecenyl acetate, 9-hexadecenyl acetate, and the like, are known pheromones or pheromone mimics for several insect species. In order to make these compounds widely available for use in insect control, economic large scale synthetic conversion processes for their preparation must be developed. While several synthetic routes for the preparation of various 9-alkenyl ester compounds have been disclosed in the prior art, the known synthetic routes are usually specific for the preparation of only one target pheromone or pheromone mimic. In addition, known synthetic routes suffer from the disadvantages of requiring multiple reaction steps with consequent low overall product yield, consumption of large quantities of reagents which do not contribute to the final product structure, and the like.
For example, in Tetrahedron, Volume 33, 1845 at 1846 (Pergamon Press 1977), Henrick describes a multi-step synthesis of 9-dodecadienyl acetate which involves: (1) the bromination of 1,8-octanediol with hydrobromic acid to give 8-bromo-1-octanol, (2) etherification of 8-bromo-1-octanol with dihydropyran, (3) alkylation of the tetrahydropyranyl ether with the lithium salt of 1-butyne while concurrently reducing the triple bond with sodium in liquid ammonia, and finally (4) the tetrahydropyranyl ether is converted to the desired acetate with acetyl chloride and glacial acetic acid. Variations of this synthetic scheme which require an even greater number of reaction steps are also disclosed by Henrick.
In Synthesis, 1977, pages 817-836, Rossi reviews synthetic methods employed for the preparation of pheromones. Pheromones having 9-Z-configuration are prepared by reaction of a solution of an appropriately selected carbonyl compound in hexamethylphosphoric triamide with an ylid obtained by reacting the corresponding phosphonium salt with the products of the reaction between potassium metal and hexamethylphosphoric triamide. While high stereoisomeric purity products are obtained, reaction yields are low and the reagents employed are expensive.
In summary, due to the large number of reaction steps required, the relative inavailability or high expense of many needed reagents, and the step wise fashion in which the desired carbon backbone is constructed, known synthetic routes for the production of 9-alkenyl esters are not amenable to being carried out economically on a large scale.